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The risk of flooding from dam failure in Los Gatos appears to be mainly from four reservoirs, all tying into the Los Gatos Creek at some point or another. Recently Clair found a great resource for better understanding this risk, and we wanted to share it with our readers.

  • There’s an interactive map (link below) that shows most, maybe all, of our Santa Clara County dams and where flooding could happen should the dam fail
  • Additionally, Valley Water has in depth info on a downloadable PDF that actually shows how deep the flooding could be (link below)
    • Some areas of Los Gatos could experience 20′ of flooding or more in case of a breach at Lexington
    • This level of information is not part of the disclosures we get when buying and selling homes. Instead it is listed as “in” or “not in” an inundation from dam failure zone

The usual home seller disclosures include a natural and environmental hazard report, but the info does not go into deep detail. For instance, it may state that a location is in a zone of potential flooding from dam failure, but it does not tell the reader which dam it is. At times I’ve sold homes that were in that designated area but wondered whether the dam was a smaller or larger one (my concern being how much water could come through).

Now, more of those questions can be answered by visiting the state of California’s Dam Breach Inundation Map Web Publisher.

Dam failure flood zones in Santa Clara County


This site is very easy to use and to understand. The dams are marked with colors to indicate the downstream risk. Larger dams that spill into more populated areas appear to be those at higher risk, but perhaps they have a different formula for that designation.

Once you zoom in to your desired area (most counties appear to be participating, and MOST dams appear to be included in this publication), just click on the colored box and wait for the information to populate. It is sometimes a little slow, but after a few seconds it will appear.

Risk of flooding from dam failure in Los Gatos

In Los Gatos there are only a few dams that seem to put the town’s area at risk (red boxes on the website). Most of them do connect to the Los Gatos Creek.

  • Rinconada
  • Vasona Lake
  • James J. Lenihan (Lexington Reservoir)
  • Austrian (in the Santa Cruz Mountains, upstream from Lexington and Vasona)

The dam at Vasona Lake doesn’t hold an enormous amount of water, and if you visit the website you’ll find that the areas of potential flooding are more limited, but do include the neighborhood of homes just below the dam, unsurprisingly. The James J Lenihan Dam at Lexinton Reservoir, though, is a large capacity reservoir, and the area for potential flooding is immense. It’s hard to see on the image below, but a good portion of Highway 85 would be inundated in this scenario as well as much of the valley between there and the bay.


Risk of flooding from dam failure in Los Gatos - map of the areas at risk should the dam at Lexington Reservoir fail


How deep could the risk of flooding from dam failure in Los Gatos be?

Most of the inundation maps simply show blue for the areas expected to flood. In many cases, inundation people think of it as damage to a home with an annoying (but not life threatening) amount of water, but in some areas of town, the risk is water 20 feet deep or more. I was quite alarmed when I found this to be the case.

Please also check out the Valley Water page on the Lexington Reservoir and Lenihan Dam.

Here there are images in the download which include a legend of how deep the water could be. Additionally, it will share how long it would take for the wave of water to begin to arrive.  With real estate transactions, we do not get this level of detail. We are told only that a property is “in” or “not in” an area of potential flooding from dam failure. But who wouldn’t want to know if we were talking about one foot or 20 feet?

The image below is of the area just north of the Vasona Dam and the situation would be a flood from Lexington. (There are 3 dams on the Los Gatos Creek, including the Austrian, which is further up in the hills, the Lenihan, and of course the Vasona Dam).


Map - inundation - Valley Water - small segment of area near the JCC

Here there are two links, and they go to PDFs you must download to view. The image above is a snippet of one page below the Vasona dam that includes the area near the JCC along Oaka Road.

Lots of questions arise for me: how would residents and workers there know about a dam breach and impending flood? If I’m not mistaken, the only way out is via Oka Road to Lark Avenue.  Can other escape routes be created? 

Inundation maps: risk of flooding from dam failure in Los Gatos
Inundation Map of Hypothetical Fair Weather Failure of Lenihan Dam (index map)
Inundation Map of Hypothetical Fair Weather Failure of Austrian Dam and Lenihan Dam (index map)

I made a tiny URL for the first one:

Natural and Environmental Hazards in addition to risk of flooding from dam failure in Los Gatos

In Silicon Valley there are few areas, if any, in which there are no natural or environmental hazards. Sometimes people tell me that they want to live in Los Gatos, but don’t want to be in an earthquake zone. Often where we see the beautiful hills, there are earthquake faults running through them or near them.  Where we have hills with brush and trees we also have a fire risk. Most of the Santa Clara Valley is in a liquefaction zone (most of Los Gatos is not in that zone).

The risk of flooding from dam failure in Los Gatos is not one which requires insurance by the home buyer’s lender (purchasing in a 100 year flood plain does trigger that requirement, though). Even so, it wouldn’t be a bad idea to carry flood insurance. About 25% of floods in the U.S. are in areas outside of the 100 year flood plain, and  regular homeowner’s insurance may not cover floods from dams that fail. Do check!

Related reading

Defensible space for fire resistance (this site)

Silicon Valley Liquefaction Zones (our Valley of Heart’s Delight blog)

Is your home safe in an earthquake? (our relo site, Move2SiliconValley)

Is there a radon risk in Silicon Valley homes? (our Valley of Heart’s Delight blog)